It measures roughly eleven metres from north to south and five metres across, rising to about a metre at its southern end, with a slight curve bending westward at the northern tip. That modest outline is the only surface trace of a fulacht fia, a type of prehistoric cooking site found in their thousands across Ireland, typically dating to the Bronze Age.

The mechanics of a fulacht fia are straightforward once explained. A trough, usually timber-lined or cut into the ground, would be filled with water; stones were heated in a nearby fire and dropped into the trough until the water boiled, allowing meat to be cooked. The shattered, heat-spent stones were discarded to one side after each use, and over generations those discarded fragments accumulated into the distinctive horseshoe-shaped or linear mounds that survive today. This example at Croagh follows the linear form, oriented on a north-south axis and positioned about ten metres west of a stream, which would have provided the water essential to the whole process. That proximity to a water source is characteristic of the type, and it sits within a wider field system in the same area, suggesting the landscape here was actively worked and organised during prehistory.